Leaving scores of sneezing, fatigued and feverish victims in its wake, the flu virus has rampaged across the United States this season, although by some indicators the number of cases may have peaked.

As of Jan. 12, 674 people from 36 counties had been hospitalized with the flu in Colorado. Four children have died, all from the Front Range.

The virus started to emerge in October, about one month earlier than normal, experts say. Outbreaks in larger cities like Boston and Chicago came as a startling jolt after the mild 2011-12 season. The Denver metro area experienced temporary vaccine shortages earlier this month.

Influenza B has been the most prevalent strain in Colorado, said Anne Christian, a pediatrician at Southwest Memorial Primary Care. Other variants are H3N2 and H1N1, commonly known as swine flu.

According to Center for Disease Control statistics, between 5 and 20 percent of U.S. residents contract the flu on a given year and more than 200,000 people are hospitalized nationally. Between 1976-2006, estimates of flu-associated deaths varied from a low of 3,000 to a high of 49,000. Young children, pregnant women and the elderly are vulnerable subgroups.

The virus is transmitted by contact - touching a keyboard, phone or door handle, for example, and then touching one's face - or by air, as when an infected person sneezes nearby.

Marc Meyer, infection control specialist at Southwest Memorial Hospital, said he's noticed an uptick in people reporting flu-like symptoms, but only three patients have been hospitalized: one adult and two children, and the blood sample came back negative for one of the kids.

"We've quit testing now. At this point we're treating symptoms," Meyer said. "Really the best response to symptoms is to stay home and not spread the sickness to other people."

He speculated that the Four Corners' relative isolation is part of why outbreaks don't spread as quickly here compared to densely populated areas.

"One of the theories about early outbreaks on the East Coast is Hurricane Sandy," he said. "We congregated so many people in relief shelters who may or may not have had vaccine. Volunteers came in from other parts of the country to help, who may not have had vaccine either. It may have created a hotbed for flu. It makes sense in theory."

While flu season could have already reached its pinnacle, Meyer recommended a flu shot through April for anyone over six months. Tamiflu is a prescribed antiviral drug that can alleviate symptoms within 48 hours of onset.

This year's vaccine is pegged at 62 percent effective by the CDC, although immunity isn't at full strength until two weeks after the shot.

With their weaker immune systems, people 65 and older are more likely to contract flu even with a shot, but the shot can suppress symptoms enough to avoid a hospital stay or worse. Meyer recommended that seniors get a Fluzone high-dose shot, which contains four times as much antigen. The high-dose was introduced only two years ago, so scientists won't have clear evidence about its benefits until 2014.

"But we do know that it's safe," Meyer said, calling the belief that the vaccine actually causes flu a "fallacy" because the dose contains only select proteins.

Christian said the flu virus, like other pathogens, spreads more quickly around the world nowadays because of airline travel and cargo shipping. The CDC and World Health Organization keep tabs on the virus year-round to try to predict what next season's strain will look like. The manufacturing of vaccines can start as early as February for delivery in August.

"You can't start a vaccine assembly line and pop it out at the end of the day. The incubation period can take months," she said, adding that Montezuma County residents should not assume their remote enclave offers full protection.

"Given the mobility of modern America and number of tourists, it behooves the community to not think of themselves as too sheltered. I still recommend shots for everyone," she said.

Meyer and Christian both encouraged parents to be on the lookout for a second illness called respiratory syncytial virus (RSV), which can clog the airways of young children with mucous and make breathing labored. It is most common in children under five, since their chest cavities and airways are smaller. Kids with a history of asthma are especially vulnerable.

Susan Ciccia, director of health services for Montezuma-Cortez Re-1, said the school district saw a spike in norovirus cases in December, but influenza hasn't been too serious of a problem yet.

"We haven't seen the absenteeism that accompanies flu symptoms," Ciccia said. "But it could emerge at any time."

Bridge Emergency Shelter had a wave of sickness from Thanksgiving to Christmas, but manager Donna Boyd thought it had "run its course."

"We try to keep things disinfected. We bleach every day and push personal hygiene. We do have one room I try to hold for quarantines," Boyd said. "It's tough to avoid. We have people breathing on each other, sitting at the same table passing plates, playing cards. There are 15 people who sleep in the same room. We just try to keep the place as clean as possible."

Pharmacies at City Market and Safeway still have vaccines available, but Walmart does not. Walgreens is expecting a new shipment by the end of this week or early next week. Meanwhile, the county's public health department has a limited supply, for children only.

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